1. Field of the Invention
The present invention relates to an organic light emitting display device and a driving method thereof, and more particularly to an organic light emitting display device and a driving method thereof, which solve problems due to a life time variation of red, green, and blue organic light emitting diodes.
2. Discussion of Related Art
Recently, since liquid crystal display devices and organic light emitting display devices have lightweight and thinness characteristics, they have been widely used in a field of portable information devices. In particular, since light emitting display devices have greater useful temperature range, higher resistance to shock or vibration, a wider angle of visibility, and a higher response speed in comparison with other flat plate display devices including liquid crystal display devices, they have been proposed as the next-generation planar type display devices.
In general, in an active matrix type organic light emitting display device, one pixel includes R, G, and B unit pixels. Each of the R, G, and B unit pixels includes an organic light emitting diode. In each organic light emitting diode, an R, G, or B organic emission layer is sandwiched between an anode electrode and a cathode electrode. Light is emitted from the R, G, or B organic emission layer by a voltage applied to the anode electrode and the cathode electrode in the organic light emitting diode.
FIG. 1 is a block diagram showing a conventional active matrix type organic light emitting display device 10.
With reference to FIG. 1, the conventional active matrix type organic light emitting display device 10 includes a display region 100, a gate drive circuit 110, a data drive circuit 120, and a controller (not shown). The display region 100 includes a plurality of scan lines 111 to 11m, a plurality of data lines 121 to 12n, and a plurality of power supply lines 131 to 13n. Scan signals S1 to Sm from the gate drive circuit 110 are provided to the plurality of scan lines 111 to 11m. The plurality of data lines 121 to 12n provide data signals DR1, DG1, DB1 . . . DRn, DGn, and DBn. The plurality of power supply lines 131 to 13n provide source voltages VDD1 to VDDn.
The display region 100 includes a plurality of pixels P11 to Pmn. The plurality of pixels P11 to Pmn, which are arranged in a matrix, are connected to the plurality of scan lines 111 to 11m, the plurality of data lines 121 to 12n, and the plurality of power supply lines 131 to 13n. Each of the pixels P11 to Pmn includes 3 unit pixels, namely, R, G, and B unit pixels PR11, PG11, PB11 . . . PRmn, PGmn, and PBmn, which are connected to one corresponding scan line, one corresponding data line, and one corresponding power supply line among the plurality of scan lines 111 to 11m, the plurality of data lines 121 to 12n, and the plurality of power supply lines 131 to 13n. 
For example, a pixel P11 disposed at an upper left end of the display region 100 includes an R unit pixel PR11, a G unit pixel PG11, and a B unit pixel PB11. Further, the pixel P11 is connected to a first scan line 111 among the scan lines 111 to 11m, a first data line 121 among the data lines 121 to 12n, and a first power supply line 131 among the power supply lines 131 to 13n. 
That is, an R unit pixel PR11 is connected to a first scan line 111, an R data line 121R among the first data lines 121 to which a data signal DR1 is provided, and an R power supply line 131R among first power supply lines 131. A G unit pixel PG11 is connected to the first scan line, a G data line 121G among the first data lines 121 to which a G data signal DG1 is provided, and a G power supply line 131G among first power supply lines 131. A B unit pixel PB11 is connected to the first scan line 111, a B data line 121B among the first data lines 121 to which a B data signal is provided, and a B power supply 131B among the first power lines 131.
FIG. 2 is a circuit diagram of each pixel in the conventional organic light emitting display device shown in FIG. 1, which shows a circuit arrangement of one pixel P11 configured by R, G, and B unit pixels.
Referring to FIG. 2, the R unit pixel PR11 includes a switching transistor M1_R, a drive transistor M2_R, a capacitor C1_R, and an R organic light emitting diode EL1_R. A scan signal S1 from the first scan line 111 is provided to a gate of the switching transistor M1_R, and a data signal DR1 from the R data line 121R is provided to a source of the switching transistor M1_R. A gate of the drive transistor M2_R is connected to a drain of the switching transistor M1_R, and a source voltage VDD1 from a power supply line 131R is provided to a source of the drive transistor M2_R. The capacitor C1_R is connected to the gate and source of the drive transistor M2_R. An anode of the R organic light emitting diode EL1_R is connected to a drain of the drive transistor M2_R, and a cathode thereof is connected to a ground voltage VSS.
In a similar manner, the G unit pixel PG11 includes a switching transistor M1_G, a drive transistor M2_G, a capacitor C1_G, and a G organic light emitting diode EL1_G. A scan signal S1 from the first scan line 111 is provided to a gate of the switching transistor M1_G, and a data signal DG1 from the G data line 121G is provided to a source of the switching transistor M1_G. A gate of the drive transistor M2_G is connected to a drain of the switching transistor M1_G, and a source voltage VDD1 from a power supply line 131G is provided to a source of the drive transistor M2_G. The capacitor C1_G is connected to the gate and source of the drive transistor M2_G. An anode of the G organic light emitting diode EL1_G is connected to a drain of the drive transistor M2_G, and a cathode thereof is connected to a ground voltage VSS.
Further, the B unit pixel PB11 includes a switching transistor M1_B, a drive transistor M2_B, a capacitor C1_B, and a B organic light emitting diode EL1_B. A scan signal S1 from the first scan line 111 is provided to a gate of the switching transistor M1_B, and a data signal DB1 from the B data line 121B is provided to a source of the switching transistor M1_B. A gate of the drive transistor M2_B is connected to a drain of the switching transistor M1_B, and a source voltage VDD1 from a power supply line 131B is provided to a source of the drive transistor M2_B. The capacitor C1_B is connected to the gate and source of the drive transistor M2_B. An anode of the B organic light emitting diode EL1_B is connected to a drain of the drive transistor M2_B, and a cathode thereof is a ground voltage VSS.
In the operation of the display region 100, when a scan signal S1 is applied to the scan line 111, the switching transistors M1_R, M1_G, and M1_B of R, G, and B unit pixels in the pixel P11 are driven, and R, G, and B data signals DR1, DG1, and DB1 from R, G, and B data lines 121R, 121G, and 121B are applied to the drive transistors M2_R, M2_G, and M2_B, respectively.
The drive transistors M2_R, M2_G, and M2_B provide a drive current corresponding to a difference between the data signals DR1, DG1, and DB1 applied to the gates thereof and the source voltage VDD1 provided from the R, G, and B power lines 131R, 131G, and 131B, to the organic light emitting diodes EL1_R, EL1_G, and EL1_B, respectively. The organic light emitting diodes EL1_R, EL1_G, and EL1_B are driven by the drive current applied through the drive transistors M2_R, M2_G, and M2_B to drive the pixel P11. The capacitors C1_R, C1_G, and C1_B are used to store the data signals DR1, DG1, and DB1 applied to the R, G, and B data lines 121R, 121G, and 121B.
An operation of the conventional organic light emitting display device having a construction mentioned above will be described with reference to a drive waveform of FIG. 3.
First, when the scan signal S1 is applied to the first scan line 111, the first scan line 111 is driven, and pixels P11 to P1n connected to the first scan line 111 are driven.
That is, switching transistors of R, G, and B unit pixels PR11 to PR1n, PG11 to PG1n, and PB11 to PB1n of the pixels P11 to P1n connected to the first scan line 111, are driven by the scan signal S1 applied to the first scan line 111. According to driving of the switching transistors, R, G, and B, data signals D(S1) including DR1 to DRn, DG1 to DGn, and DB1 to DBn from R, G, and B data lines 121R to 12nR, 121G to 12nG, and 121B to 121nB, constituting the first to nth data lines 121 to 12n, are concurrently applied to gates of drive transistors in the R, G, and B unit pixels, respectively.
The drive transistors of the R, G, and B unit pixels provide drive currents corresponding to R, G, and B data signals D(S1) including DR1 to DRn, DG1 to DGn, and DB1 to DBn respectively applied to R, G, and B data lines 121R to 12nR, 121G to 12nG, and 121B to 121nB, to R, G, and B organic light emitting diodes, respectively. Accordingly, when a scan signal S1 is applied to the first scan line 111, organic light emitting diodes constituting the R, G, and B unit pixels PR11 to PR1n, PG11 to PG1n, and PB11 to PB1n of the pixels P11 to P1n connected to the first scan line 111, are concurrently driven.
In the same manner, when a scan signal S2 for driving the second scan line 112 is applied, data signals D(S2) including DR1 to DRn, DG1 to DGn, and DB1 to DBn from R, G, and B data lines 121R to 12nR, 121G to 121nG, and 121B to 121nB constituting first to nth data lines 121 to 12n, are respectively applied to R, G, and B unit pixels PR21 to PR2n, PG21 to PG2n, and PB21 to PB2n of pixels P21 to P2n connected to a second scan line 112.
Organic light emitting diodes including R, G, and B unit pixels PR21 to PR2n, PG21 to PG2n, and PB21 to PB2n of pixels P21 to P2n connected to the second scan line 112 are concurrently driven by drive currents corresponding to the data signals D(S2) including DR1 to DRn, DG1 to DGn, and DB1 to DBn.
By repeating the above mentioned operation, a scan signal Sm is finally applied to an mth scan line 11m, according to data signals D(Sm) including DR1 to DRn, DG1 to DGn, and DB1 to DBn applied to the R, G, and B data lines 121R to 12nR, 121G to 121nG, and 121B to 12nB, organic light emitting diodes constituting R, G, and B unit pixels PRm1 to PRmn, PGm1 to PGmn, and PBm1 to PBmn of pixels Pm1 to Pmn connected to an mth scan line 11m, are concurrently driven.
Consequently, scan signals S1 to Sm are sequentially applied to the first scan line 111 to the mth scan line 11m. As a result, the pixels P11 to P1n through Pm1 to Pmn connected to scan lines 111 to 11m are sequentially driven to drive the pixels during one frame 1F, so that an image is displayed.
In the conventional organic light emitting display device having the configuration described above, each pixel includes three R, G, and B unit pixels. A driver, namely, a switching thin film transistor, a drive thin film transistor, and a capacitor are arranged in the R, G, and B unit pixels, and a data line and a common power line provide a data signal and a common power supply to the unit pixels.
According to a construction of the conventional organic light emitting display device, since each pixel includes three unit pixels, a plurality of wirings and a plurality of elements are arranged in every pixel, the circuit arrangement is complex, and it increases occurrence of defects, thereby deteriorating yield.
Moreover, as a display device is made with increasingly higher resolution, area of each pixel is reduced. Accordingly, it becomes difficult to arrange a plurality of elements in each pixel and the aperture ratio is reduced.
In addition, since organic light emitting diodes in R, G, and B unit pixels include emission layers formed by different materials, the life time of the organic light emitting diodes in different unit pixels are different from each other.
Accordingly, as time goes by, luminance reduction degrees are different in the R, G, and B unit pixels, thereby causing a white balance variation and an image sticking development.